1. Field of the Invention
The present invention is directed to millimeter wave antennas, and, more particularly, to a millimeter wave electronically scanned antenna.
2. Description of the Related Art
Mechanically scanned antennas classically used on millimeter wave seeker systems suffer from a variety of problems including high cost, limited scanning performance, and low reliability. Electronically scanned antennas have greatly improved scanning performance and high reliability, but using traditional techniques have been too costly to implement and suffered from low efficiency (gain). Traditional passive electronically scanned phased arrays use multi-bit phase shifters to achieve electronic beam steering. At millimeter wavelengths the loss is typically 1 dB per bit. The multi-bit phase shifting element is responsible for the high cost and low efficiency using the classical design approach.
A conventional electronically scanned antenna requires multi-bit phase shifters (between 5-8 bits) to accomplish beam steering. The insertion loss, as mentioned above, of the phase shifter at Ka band is approximately 1 dB per bit. The associated loss of the typical phase shifting element prohibits the use of the passive electronically scanned antenna in a high performance active missile radar seeker. The Active electronically scanned antenna T/R module adds amplification on both transmit and receive to mitigate the loss of the phase shifter. Additionally, the classic T/R module approach at Ka band is very demanding due to the tight spacing, low efficiency, high gain/power required to overcome losses, the high transmit/receiver isolation necessary to prevent module oscillation, and the added complexity of multi-bit phase and attenuation control.
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.